The invention relates to a method and apparatus for producing substantially monodisperse micro particles, preferably of a heat sensible material or biological active material.
U.S. Pat. No. 4,871,489 A discloses an apparatus and process for producing liquid droplets and solid particles having a narrow size distribution. Thin liquid streams are forced under pressure through a plurality of orifices in an orifice plate, the largest of the orifices having a diameter not greater than about three times the diameter of the smallest of the orifices. The thin liquid streams are oscillated to cause breakup of each stream into droplets having a narrow size distribution. These droplets are subsequently dried to become solid particles having a narrow size distribution. The apparatus and process according to U.S. Pat. No. 4,871,489 is mainly suitable for manufacturing powders of metal oxides. Although powders of metal oxide with excellent characteristics may be produced, the apparatus and process is, however, not suitable for producing powders of heat-sensible material, like e.g. pharmaceutical product. This is due to the fact that exact control of the temperature is difficult in the apparatus and process according to U.S. Pat. No. 4,871,489. Moreover, the disclosed apparatus is constructed in such a way that an efficient cleaning is almost impossible. This, of course, has less significance when dealing with metal oxide powders. However, when dealing with pharmaceutical product, which often has to be handled in sterile environment, it is a major disadvantage. Further, though claiming a narrow size distribution, the results show substantial variation. The description of the method and the examples admit that the method results in droplet impingement. It can be calculated that the velocity of the dispersion gas through the dispersion orifice is in the order of 100 m/s.